Support for biomedical implant device

ABSTRACT

A support for a biomedical implant device in which the support has a surface layer composed of a biocompatible calcium phosphate material such as sintered hydroxyapatite with a porosity of 50-60% and pore size of 0.5-500 micrometers. Preferably, the surface layer is formed with projections or recesses of a few hundred micrometers size.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a support for retaining biomedicalimplant devices such as a catheter for peritoneal dialysis, anextracorporeal shunt for hemodialysis, a tube for an ascitesrecirculation circuit, a drain tube, an air tube for an artificialheart, an electric circuit tube, and drug reservoir to be implantedunder the skin. In particular, the present invention relates to asupport for such biomedical implant devices that manifests enhancedbiocompatibility and which allows them to be retained in the body over aprolonged period without permitting bacterial ingress.

2. Background of the Invention

An example of the support conventionally used to fix a biomedicalimplant device in the human body is a cuff which is used with a catheterfor peritoneal dialysis. As shown in FIG. 1, a catheter 1 is insertedthrough the skin 10 of the patient, the subcutaneous layer of fat 11,the fascia 12, the muscular tunic 13 and the peritoneum 14. The catheter1 is retained in the body so as to permit injection or discharging of adialyzing solution through the catheter 1. In this case, a cuff 2attached to the catheter 1 is used as a support for functionallyretaining the catheter 1 in the body over an extended period and isgenerally sutured in living tissues at the end of a surgical operation.The cuff 2 is typically made of such materials as knitted or unknittedfabrics of synthetic or natural fibers, plastic or plastic film.

Another prior art biomedical implant device proposed to date is a drugreservoir for subcutaneous implantation. As shown in FIG. 2, a reservoir15 is implanted below the skin layer 10 and is composed of a drug cell16. Holes 17 on projections guide a retaining thread (suture). Theintended drug is injected into the cell 16 through a silicone orsynthetic rubber wall 18. A silicon tube 19 serves as a passage forintroducing the drug into the affected site of part of the body such asa blood vessel or muscle. Stability of the retained reservoir 15 isrequired for a prolonged period in order to allow for periodic supply ofthe drug into the reservoir through the wall 18 with syringe.

Conventional supports such as cuffs that are formed of cellulosic orsynthetic fibers, plastics, titanium or silicone resins show poorbiocompatibility and poor adhesion to living tissues because of thenature of their constituent materials. As a result, during prolonged useof biomedical implant devices within the body, they might be displacedin position or bacterial ingress may occur in the gap between the deviceand the surrounding tissues.

SUMMARY OF THE INVENTION

A general object of the invention is to eliminate the above describedproblems in a biomedical implant device.

A particular object, therefore, of the present invention is to provide asupport for biomedical implant device that affords enhanced adhesion totissues and allows the implanted biomedical device to be retained stablyin the body without permitting bacterial ingress.

Another object of the present invention is to provide a support which,in addition to the enhanced adhesion to surrounding tissues, permits thetissue to be anchored in the support, with subsequent increase in thestability of the support in the body.

A further object of the present invention is to provide a supportpossessed of increased strength and enhanced adhesion to the biomedicalimplant device.

These objects are achieved by a biomedical implant device having asupport made of a biocompatible calcium phosphate compound as thematerial of the surface layer. The calcium phosphate material may beporous, thereby allowing anchoring of the tissue. To provide strength,the support is made in multiple layers. The porous or solid support mayhave in its surface many recesses formed by etching, ion milling orother techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sketch of a conventional catheter with a cuff in theimplanted state.

FIG. 2 is a sketch of a conventional drug reservoir in thesubcutaneously implanted state.

FIGS. 3, 7, 8A and 8B and 9 are cross-sectional views of cuffs accordingto four embodiments of the present invention.

FIGS. 4 to 6 are pictorial representations of supports for biomedicalimplant device in the state where they adhere to surrounding tissues.

FIG. 10 is a sketch showing a cross section of the surface layer of acuff according to a fifth embodiment of the present invention.

FIGS. 11A and 11B are a plan and a cross-sectional view, respectively,of a drug reservoir to be implanted under the skin according to a sixthembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The support for biomedical implant device of the present invention ishereinafter described in detail. FIG. 3 shows a cuff 2 prepared inaccordance with one embodiment of the present invention. A catheter 1made of a plastic or some other suitable material is connected to thecuff 2 that is formed of a biocompatible calcium phosphate material suchas sintered hydroxyapatite, bioglass or sintered tricalcium phosphate(TCP). The cuff 2 which is formed of sintered hydroxyapatite can beprepared from a hydroxyapatite powder by the following procedure. Ahydroxyapatite powder comprising irregularly shaped particles of 0.1-1μm in average size is blended with a hydroxyapatite powder comprisingspherical particles of 2-20 μm in average size. The blend is intimatelymixed with water and a blowing agent. The mix is expanded and dried in athermostatic dryer. A suitable blowing agent is an aqueous solution ofhydrogen peroxide or egg albumin.

The so prepared porous hydroxyapatite is machined into a cuff-shapedstructure which is fired at a temperature of 1,000°-1,250° C. to producethe intended cuff 2. The cuff has a porosity of 5-60%, preferably20-40%, with the pore size being adjusted to 0.5-500 μm, preferably5-200 μm. The value of the porosity is determined by comparing thedensity of the solid material with that of the porous material. Thepercentage difference is the porosity and represents generally thevolume percentage of voids. The cuff 2 is then joined to a catheter 1which is implanted in the body. Such a cuff exhibits goodbiocompatibility while it is being gradually fused to surroundingtissues with time. Any bacterial ingress that might occur via the outersurface of the catheter is completely prevented at least by the cuff 2,with the result that the catheter 1 can be stably retained in the bodyover a prolonged period.

Adjustment of the porosity and pore size of the cuff to theabove-specified values ensures spontaneous formation of small voids inits surface with the result that the effective surface area of the cuff2 is sufficiently increased to provide enhanced adhesion to thesurrounding tissues. If the porosity of the cuff is less than 5%, strongadhesion to the surrounding tissues is not attained. If the porosityexceeds 60%, the strength of the cuff 2 is drastically decreased. If thepore size of the cuff is less than 0.5 μm, tissue cells are unable toenter the cuff through voids. If the pore size exceeds 500 μm, thedesired anchoring of tissues in the porous structure of the cuff cannotbe attained.

FIGS. 4, 5 and 6 show that the adhesion between the cuff and surroundingtissues increases as the porosity of the cuff increases. As can be seenfrom the comparison of FIG. 4 (20% porosity), FIG. 5 (30% porosity) andFIG. 6 (56% porosity), strong adhesion is imparted by the tissues(colored portion) penetrating into the sintered hydroxy apatite (whiteportion).

FIGS. 7 shows a cuff according to a second embodiment of the presentinvention. A catheter 1 is connected to a cuff 2. The surface of thecuff 2 is provided with small projections 3 (5-1,000 μm in height) thatare formed by cutting or some other machining technique. The cuff 2having such small projections 3 on its surface serve as a brake orimpediment resisting movement when it is implanted in the body.Therefore, the cuff 2 with the projections 3 allows the catheter 1 to besecurely fixed in the body right after it has been implanted by asurgical operation.

FIGS. 8A and 8B show a cuff according to a third embodiment of thepresent invention. A catheter 1 is connected to a cuff 2 that isprovided with holes 3 for facilitating post-operational suturing. Twovariations of such a cuff 2 are shown in the two drawings.

FIG. 4 shows a cuff according to a fourth embodiment of the presentinvention. A catheter 1 is connected to a cuff 2 that is composed of asurface-layer portion 4 and an inner-layer portion 5. The surface-layerportion 4 is formed of a biocompatible calcium phosphate material havinga comparatively high porosity. The inner-layer portions 5 is formed of abiocompatible calcium phosphate material having a comparatively lowporosity. The inner-layer portion 6 may be formed on other materialssuch as titanium, alumina and plastics and, if plastic materials areused, greater facility is ensured when connecting the cuff 2 to thecatheter 1. The advantage of this fourth embodiment is that theinner-layer portion 6 imparts a greater strength to the cuff 2 so thatthe catheter 1 can be stably retained within the body.

FIG. 10 shows a cuff according to a fifth embodiment of the presentinvention. A catheter 1 is connected to a cuff 2 that is prepared fromsintered hydroxyapatite which is surface-treated by etching or ionmilling to form recesses 7 in its surface having diameters of 0.5-500μm. The multiple recesses 7 help increase the surface area of the cuff 2so as to provide further enhanced adhesion to surrounding tissues. Theconcept of this embodiment is applicable not only to the case where thecuff 2 has a solid structure but also to the case where it is made of aporous structure. If recesses 7 are formed in the porous surface thathas been attained by the sintering described above, the resulting cuff 2provides not only good adhesion to surrounding tissues but alsoeffective anchoring of the issue in the porous surface of the cuff 2,thereby ensuring greater stability of the catheter in the body.

FIGS. 11A and 11B shows a drug reservoir to be implanted under the skinaccording to a sixth embodiment of the present invention. Componentswhich are the same as those shown in FIG. 2 are identified by likenumerals. The reservoir 15 is surrounded by a casing 20 that has holes17 for suturing. The casing 20 is formed of a biocompatible calciumphosphate material. Any of the techniques employed in theabove-described first to fifth embodiments is applicable to the casing20 so that it will display sufficient biocompatibility and adhesion tothe surrounding tissues to ensure that the reservoir 15 is stablyretained in the body over a prolonged period.

As described in the foregoing pages, the support for biomedical implantdevice of the present invention is made of a biocompatible calciumphosphate material either entirely or at least in the part which is tocontact surrounding tissues when the device is implanted in the body. Asa result, the support has improved adhesion to the living tissues andallows the implanted biomedical device to be stably retained in the bodywithout permitting bacterial ingress.

What is claimed is:
 1. A biomedical implant device for implantationwithin tissue of a body, comprising: a support having a surface layer tobe contacted with said tissue and composed of a biocompatible calciumphosphate material; and a medically operative part at least partiallyenclosed by said surface layer.
 2. A biomedical implant device asrecited in claim 1, wherein said calcium phosphate material is sinteredhydroxyapatite.
 3. A biomedical implant device as recited in claim 1,wherein said calcium phosphate material has a porosity of 5-60%.
 4. Abiomedical implant device as recited in claim 3 wherein said porosity isin a range of 20-40%.
 5. A biomedical implant device as recited in claim2, wherein said calcium phosphate material has a porosity of 5-60%.
 6. Abiomedical implant device as recited in claim 1, wherein said calciumphosphate material has a porosity of 5-60% and has voids with an averagepore size of 0.5-500 micrometers.
 7. A biomedical implant device asrecited in claim 6, wherein said average pore size is 5-200 micrometers.8. A biomedical implant device as recited in claim 2, wherein saidcalcium phosphate material has a porosity of 5-60% and has voids with anaverage pore size of 0.5-500 micrometers.
 9. A biomedical implant deviceas recited in claim 8, wherein said average pore size is 5-200micrometers.
 10. A biomedical implant device as recited in claim 1,wherein said support further comprises at least one inner layer insidesaid surface layer of a material of greater strength than said surfacelayer.
 11. A biomedical implant device as recited in claim 10, whereinsaid inner layer comprises sintered hydroxyapatite with a porositysignificantly less than that of said surface layer.
 12. A biomedicalimplant device as recited in claim 1, wherein said surface layerincludes a plurality of surface projections having a average height of5-1000 micrometers.
 13. A biomedical implant device as recited in claim5, wherein said surface layer includes a plurality of surfaceprojections having heights of 5-1000 micrometers.
 14. A biomedicalimplant device as recited in claim 1, wherein said surface layerincludes a plurality of surface recesses having diameters of 0.5-500micrometers.
 15. A biomedical implant device as recited in claim 5,wherein said surface layer includes a plurality of surface recesseshaving diameters of 0.5-500 micrometers.
 16. A biomedical implant deviceas recited in claim 1, wherein said medically operative part comprises acatheter and said support acts as a cuff surrounding said catheter. 17.A biomedical implant device as recited in claim 1, wherein saidmedically operative part comprises a drug reservoir and said support atleast partially covers said drug reservoir. .Iadd.
 18. A biomedicalimplant device for implantation within the tissues of a body,comprising; a support in the form of a cuff having a surface layer to becontacted with said tissues and composed of a biocompatible calciumphosphate material. .Iaddend. .Iadd.19. A biomedical implant device forimplantation within the tissues of a body, comprising; a support havinga surface layer to be contacted with said tissues and composed of abiocompatible calcium phosphate material, said support being in the formof a catheter cuff, said cuff including fixing means which, in use,operates to stably retain a catheter within the body. .Iaddend..Iadd.20. A drug reservoir device for implantation within the body of adrug recipient, comprising; a drug reservoir, a casing formed of abiocompatible calcium phosphate material and substantially covering atleast one surface of said reservoir and being in contact with tissues ofthe body in use, a drug entry location for receiving quantities of adrug to be delivered to the body, and a drug exit location through whichsaid drug is supplied to the body. .Iaddend. .Iadd.21. A biomedicalimplant device for implantation within the tissues of a body,comprising; a support in the form of a catheter cuff having a surfacelayer to be contacted with said tissues and composed of a biocompatiblecalcium phosphate material. .Iaddend. .Iadd.22. A biomedical implantdevice for implantation within the tissues of a body, comprising; asupport having a surface layer to be contacted with said tissues andcomposed of a biocompatible calcium phosphate material, said supportbeing in the form of a cuff, said cuff including fixing means which, inuse, operates to stably contact a member to be held in place in the bodyby said cuff. .Iaddend. .Iadd.23. A device as claimed in claim 22,wherein said fixing means includes an interior surface of said cuff..Iaddend. .Iadd.24. A drug reservoir device for implantation within thebody of a drug recipient, comprising: a drug reservoir, a casing formedof a biocompatible calcium phosphate material and substantially coveringa surface of said reservoir and being in contact with tissues of thebody in use, a drug entry location for receiving quantities of a drug tobe delivered to the body, and a drug exit location through which saiddrug is supplied to the body. .Iaddend.